1. Field of the Invention
The invention relates to an engine starter apparatus, and more particularly to an improvement in an engine starter drive system from a crankshaft to a starter motor.
2. Related Art
A conventional engine starter apparatus is constructed as shown in FIG. 8. A ring gear 3 mounted on a crankshaft 2 of an engine 1 is engaged with a pinion 6 mounted on an output rotating shaft 5 of a starter motor 4 so that the ring gear 3 is rotated to start the engine 1.
It should be noted that the crankshaft of the engine is rotated by changes in the torque of the engine caused by the strokes such as intake, compression, power, and exhaust. This process similarly applies when the crankshaft is rotated to start the engine. That is, the crankshaft also undergoes the same changes in its rotational torque. As a result, a motor section of the starter motor, which imparts a rotational force to the crankshaft when the engine is to be started, is rotated acted upon by the changes in the torque. A current value flowing at the motor section of the starter motor which undergoes such changes in the torque changes in proportion to the torque as shown by the solid line shown in FIG. 6.
As shown in FIG. 7, the starter output characteristic (torque x rotational speed) of the starter motor generally depicts a heap as the current value increases with increasing load. A starter requirement is to be responsive to changes in the torque of the crankshaft, i.e., the current value shown in FIG. 6. In other words, a cranking speed which allows ignition must be ensured in the engine compression stroke (engine torque is at maximum). Thus, the motor section has heretofore been designed so that its operation range falls on a predetermined range (current values I'min to I'max) in the left side of the starter output curve shown in FIG. 7 which is close to the peak (maximum starter output). Accordingly, conventional engine starters, installed in passenger cars with torque changes that are comparatively large, are quite large and heavy.
In addition, in response to the changes in the torque of the engine, both the engine cranking speed and the starter cranking speed undergo changes, thereby causing abnormal sounds at various parts of the starter, ring gear, and the like.
The subject invention has been made to overcome the above conventional problems. Accordingly, an object of the invention is to provide an engine starter apparatus which is not only capable of using a small starter motor even for an engine with large changes in torque, but also free if noise from the gear ring and various parts of the starter.